Methods: A total of 54 CA-MRSA were investigated: 48 being recent clinical isolates from community sources within Europe and further defined as CA-MRSA by cefoxitin 30 mg disc zone of inhibition ≤19 mm, possessing staphylococcal cassette chromosome mec type IV or IVa and having full susceptibility to gentamicin (GEN). The remaining 6 were CA-MRSA reference isolates from the Network on Antimicrobial Resistance in Staphylococcus aureus (NARSA) collection. MIC was determined for NXL101, GEN, azithromycin (AZI), clindamycin (CLI), dalfopristinquinupristin (DQ), daptomycin (DAP), levofloxacin (LFX), linezolid (LZD) and vancomycin (VAN) by CLSI broth microdilution.

Results: Summary MIC data are shown in the table. NXL101 was the most active agent against CA-MRSA. A high percentage of resistance was observed to LEV and AZI, but full susceptibility was shown to most other agents apart from CLI.

Percentage

MIC (mg/L)

Suscep tible

Inter mediate

Resistant

MIN

50%

90%

MAX

NXL101







<0.015

0.06

0.12

0.5

AZI

44.4

0

55.6

0.25

>64

>64

>64

CLI

75.9

0

24.1

0.06

0.12

>8

>8

DQ

100

0

0

0.25

0.25

1

2

DAP

100





0.12

0.5

1

1

GEN

100

0

0

0.12

0.25

0.5

0.5

LEV

22.2

0

77.8

0.12

8

16

>32

LM

100





0.5

2

2

4

VAN

100

0

0

0.5

1

1

1

Conclusion: NXL101 showed excellent activity against CA-MRSA, and may offer a viable alternative for the treatment of CA-MRSA and other S. aureus infections in the future.